Knowing the identity of a user visiting a website may be useful for several reasons. For example, many websites display advertisements to users. Typically, advertisements may be more effective if they are targeted to a user's personal preferences and/or interests. In order to target an advertisement to a particular user viewing a website, the website server needs to know additional information about the user. One example of information that a website server may track is the set of pages visited by the user. An example of information that an advertising server may track is the set of advertisements displayed to a user and the set of advertisements clicked by the user. Website servers and advertisement servers can display relevant content or advertisements to a user if they have access to such information. Typically, website servers and advertisements servers use a browser cookie to store the identity of a user.
However, once the cookies are cleared from the user's browser, the website server may no longer be able to determine the identity of the user. For example, a website server may receive a web request from a browser of a user, but without any other information, the website server may be unable to determine the user's identity, preventing the website server from displaying advertisements targeted specifically to the user.
Additionally, knowing the identity of a user may be useful for a website server to determine statistics about traffic on the server. For example, it may be useful to know the identities of users so that a website server can determine whether a particular web request is received from a new user or from a user who previously visited the website. However, determining the identity of a user visiting a website of a website server may be especially difficult for web servers which primarily experience guest traffic (e.g., websites which are more likely accessed without a user having to log in to a user account for the website).